Combining info and spatial directivities in multiple antenna transmission systems

It is well known that Massive MIMO systems (Multiple-input multiple-output) have high potential for future wireless broadband systems. However, high spectral and power efficiency requirements can be only achieved by multilevel modulations and efficient power amplification. This seems contradictory, due envelope variation of multilevel constellations that can compromise efficiency of power amplification. These restrictions can be overpassed by a multi-amplifier/antenna transmitter compatible with efficient and low cost saturated nonlinear amplifiers combined with a frequency-domain receiver for broadband millimeter wave systems. Based on this multi-amplifier structure it is possible to define a double layered structure where each amplification branch is connected to an antenna array to achieve both constellation and power directivities, assuring at same time similar performances to systems using transmitters with 2-dimensional antenna arrays.